The present invention relates to a heat fixing roll for so-called electronic copying machines such as electrostatic copying machines, laser printers and the like. The present invention also relates to a method of producing the roll.
Such a heat fixing roll is generally manufactured as shown in FIG. 7 to 9.
As shown in FIG. 7, an insulating layer 2 is formed on the surface of a hollow tube 1, and a metal wire 3 is helically wound on the insulating layer 2 formed, a heating resistor layer 4 being formed on the surface of the insulating layer 2 by thermal spray coating a resistor material. The metal wire 3 is then removed to form the screw-like heating resistor 4a shown in FIG. 8. As shown in FIG. 9, a reinforcing insulating layer 5 and an antisticking layer 6 are formed in turn on the surface of the heating resistor 4a.
Conventional fixing rolls for copying machines and the method of producing the rolls have the following problems:
(1) When the metal wire 3 is helically wound on the insulating layer 2 outside the hollow tube, the hollow tube is rotated so that the metal wire 3 closely adheres to the insulating layer 2, and the metal wire 3 is tensed so as not to slide thereon and is moved at a predetermined speed along the hollow tube while being balanced so as not to be cut.
The winding work is therefore complex and delicate and thus takes much time, as well as being incapable of easily winding the wire 3 in accordance with setting.
(2) Since the metal wire 3 does not closely adhere to the insulating layer 2, if the wire size of the metal wire 3 is, for example, 100 to 200 .mu.m, since the adjacent portions of the groove formed are incompletely separated from each other at the bottom, the adjacent portions of the heating resistor are sometimes connected to each other at the bottom. In order to prevent the connection at the bottoms of the groove, it is necessary to use a metal wire having a large size, for example, 350 to 700 .mu.m.
However, the use of such a thick metal wire causes the formation of a groove having a width of 400 to 700 .mu.m and thus often causes the formation of a depressed helical line 6a on the surface of the antisticking layer 6.
In order to remove such a depressed line 6a, it is therefore necessary to grind the surface of the antisticking layer 6 until the smooth plane 6b shown by a one-dot chain line in FIG. 9 is formed.
The antisticking layer 6 must be thus coated so as to have a thickness which is greater than the required thickness by a thickness corresponding to the layer to be ground. In addition, the need for the grinding process causes an increase in production cost.